A problem which has been posed in recent years in the pharmaceutical sector is that there is a great variety of active compounds which are characterized fundamentally, in that they cannot be administered by oral route. The main causes why these compounds cannot be administered by this route are: a) rapid enzymatic and metabolic degradation; b) chemical and biological instability; c) low solubility in aqueous medium; and/or d) limited permeability in the gastrointestinal tract.
Examples of such active compounds include: a) Peptidic-type (peptide) macromolecules such as insulin, interferons or calcitonins; b) Saccharidic-type (saccharide) macromolecules such as heparin or, heparins and derivatives such as LMWH (Low Molecular Weight Heparins), pentasacharides; and c) other types of smaller hydrophilic molecules such as salbutamol or acyclovir.
Heparins are anticoagulants which act by the inactivation of certain coagulation cascade factors. Heparins are essentially used for their anticoagulant (related with the inhibition of factor IIa) and antithrombotic (by the inhibition of factor Xa) properties for the prevention and the treatment of thromboembolic diseases (Low- and ultra-low-molecular-weight heparins. Best Pract. Res. Clin. Haematol. 2004; 17: 77-87). In prevention, they are used to reduce the incidence of thromboembolic complications after prolonged immobilization due to a disease, and after surgical interventions (Prevention of venous thromboembolism. Agnelli and Sonaglia., Thromb Res. 2000, 97: V49-62), and in curing, they are used for the treatment of deep vein thrombosis (Treatment of venous thromboembolism. Ageno. Thromb Res. 2000, 97: V63-72.), of pulmonary embolisms, of disseminated intravascular coagulation, acute arterial obstruction and the acute phase of myocardial infarction.
Currently, heparin is extracted from porcine or bovine intestinal mucosa (Heparins: all a nephrologist should know. Hetzel et al. Nephrol Dial Transplant. 2005; 20: 2036-42). The unfractionated heparin is a heterogeneous mixture of sulfated mucopolysaccharide chains whose molecular mass is between 3,000 and 30,000 daltons. Its average molecular mass is 15,000 Daltons, and it corresponds to a heparin molecule of around 45 osidic units (Molecular weight dependency of the heparin potentiated inhibition of thrombin and activated factor X. Effect of heparin neutralization in plasma. Andersson et al. Thromb Res. 1979; 15: 531-41).
Heparin acts by the intermediation of a cofactor: antithrombin III (ATIII), which is a natural plasma inhibitor of coagulation (Heparin and Low-Molecular-Weight Heparin: The Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy. Hirsh and Raschke. Chest. 2004; 126: 188S-203S) and it behaves as a catalyst with respect to ATIII. ATIII has a slow and progressive action. Once the heparin has been fixed to the ATIII by the intermediation of the pentasaccharide fragment, this action becomes immediate. This fixation causes a change in the formation of the ATIII which then permits the irreversible fixation thereof on the active site of serine proteinase-type coagulation factors (factors IIa, Xa and IXa, mainly). Then, heparin is released intact, and can then react with a new antithrombin molecule.
It should be mentioned that the pharmacodynamic effect of heparins depends on the chain length of oligosaccharides. Indeed, to inhibit the thrombin, heparin should be fixed on ATIII and on thrombin through a pentasaccharide block. On the other hand, to inhibit factor Xa, heparin should only fix to ATIII by the pentasaccharide block. Thus, the fragments with a molecular mass (MM) below 5,400 Da, i.e. 18 saccharide units, lose their capacity to be simultaneously fixed to thrombin and ATIII, and will thus have an essentially anti-Xa activity. The fragments with a MM greater than or equal to 5,400 Da will be both anti-Xa and anti-IIa. Standard heparin comprises fragments with a variable molecular mass of 2,000 to 30,000 Da, and therefore has activity on the two factors, Xa and IIa (Heparin and Low-Molecular-Weight Heparin: The Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy. Hirsh and Raschke. Chest. 2004; 126: 188S-203S). It therefore has both an antithrombotic and an anticoagulant activity, in comparison with low molecular weight heparins, which are essentially antithrombotic agents with a predominance of anti-Xa activity.
Venous thromboembolic disease continues to be responsible for important morbidity and and/or mortality. In fact, in the United States, the number of persons hospitalized for this reason is estimated at between 300,000 and 600,000 per year. Furthermore, this disease, due to the pulmonary embolism of which it is the cause, would be responsible for 50,000 (Development of oral heparin therapy for prophylaxis and treatment of deep venous thrombosis. Money and Gorka. Caridovasc Surg. 2001; 9: 211-8) to 100,000 deaths per year in the United States (Prevention of venous thromboembolism. Agnelli and Sonaglia. Thromb Res. 2000, 97: V49-62).
Additionally, pulmonary embolism can be produced without clinical venous thrombosis, henceforth the interest in prevention with regard to patients with a risk of thrombosis, among which are: cancer, age over 70, prolonged immobility, paralysis, obesity or even taking estrogens by oral route.
Since heparin acts on the coagulation factors by a catalysis mechanism mediated by ATIII, the measurement of its plasma concentration does not constitute an efficient means to determine its biological activity. The procedures used should instead reflect heparin's capacity to inhibit factors Xa and IIa. For this reason, different measurement process can be used in human beings and animals: a) the measurement of the coagulation factor activity, expressed in units of inhibition of Xa or IIa activity; b) the measurement of the haemorrhaging time determined by the activated partial thromboplastin time (aPTT) (This test explores the intrinsic route of the coagulation measuring the coagulation time of decalcified and platelet-impoverished plasma in the presence of a platelet equivalent (cephalin) and calcium.); and c) the measurement of the prothrombin time exploring the intrinsic coagulation route (This procedure uses recalcified blood plasma in the presence of tissue thromboplastin; Digestive absorption of heparin with alternative formulations. Ubrich et al., 2002. S.T.P. Pharma Sciences. 2002; 12: 147-55). There is another process which only exists in animals, and consists of measuring the variation in the size of a thrombus. This does not permit quantifying the response, but it shows if there is a proven pharmacological action of the anticoagulant.
Insulin is the “anabolic” hormone par excellence; i.e. it permits providing the cells with the sufficient supply of glucose for the synthesis process with energy expenditure, which will then, through glycolysis and cell respiration, produce the necessary energy in the form of ATP (adenosine triphosphate mononucleotide) which uses the metabolism as unit of transportable energy for said processes. It maintains the glucose concentration in our blood. It achieves this because when the glucose level is high the pancreas releases it into the blood. Its function is to favor the cell absorption of glucose.
It is one of the two hormones produced by the pancreas together with glucagon (unlike insulin, when the glucose level decreases it is released into the blood). Insulin is produced in the pancreas in the “Islets of Langerhans”, by cells called Beta cells. One way of detecting if the Beta cells produce insulin is by carrying out a test, checking for the presence of C-peptide in the blood. C-peptide is released into the blood when the Beta cells process the proinsulin, converting it into insulin. Only when between 10% and 20% of the Beta cells are in good condition, symptoms of diabetes begin to appear, first passing through a prior state called honeymoon where the pancreas still secretes some insulin.
Normally, the insulins currently used are synthesized by means of genetic engineering through recombinant DNA technology, due to the fact that a rapid, medium or slow activity is pursued. In type I diabetes, and in some cases of type II, it is necessary to inject insulin to maintain a correct glucose level in the blood. The following types of insulins exist: a) quick-acting insulins; b) intermediate-acting insulins or NPH; c) slow-acting insulins; and d) 24-hour insulins.
Insulin types can also be categorized by the site of administration: a) injectable subcutaneous insulin formulations, which include any insulin, whether quick-acting or delayed; b) injectable endovenous insulins formulations, which include: only quick-acting insulins that do not have retarders; c) inhalable insulin formulations, which despite being as efficient as the traditional one, eliminates the need of being injected to the patient. However, there is no insulin formulation on the market that can be administered by orally to provide sufficiently high bioabsorption, thereby highlighting the need for an oral solid formulation.
Although some of these compounds can be administered orally, they have very low and/or very erratic gastrointestinal absorption, which poses a serious problem for marketing these type of drugs, because the results obtained differ greatly from those expected due to their behavior in LADME (Liberation, Absorption, Distribution, Metabolism and Elimination) pharmacokinetic processes. Furthermore, these macromolecules are hydrophilic and very poorly permeable across the mucosa, which results in low mucosal absorption, in the case of the oral route. This is worsened since these macromolecules have to pass through the stomach.
The digestive mucosa allows small lipophilic molecules to pass through, but it is very impermeable to charged hydrophilic macromolecules. Furthermore, the digestive tract is coated with negatively charged mucosa, which has a natural tendency to repel the molecules of the same charge.
A clear example of an active compound whose absorption is limited following oral administration is heparin. After oral administration, absorption through the digestive mucosa is not limited by its solubility but by its low permeability with respect to the intestinal membrane, mainly due to its negative charge. The permeability of heparins through the digestive epithelium is, therefore, very low, which makes the administration of heparin/formulations containing heparin by oral route very difficult.
For this reason, the route of administration chosen in the majority of the aforementioned classes of compounds is parenteral administration, mainly via intramuscular or subcutaneous injections. At present, some of these compounds are even administered via nasal and pulmonary formulations as in the case of salmon calcitonin or insulin (Alpar, H. J.; Somavarapu, S.; Atuah, K. N.; Bramwell, V. W. Adv. Drug Deliv. Rev. 2005, 57, 411-430; Paltz, R. M.; Patton, J. S.; Foster, L.; Mohammed, E. USA Appl. No 355578).
Nevertheless, a problem posed by non-oral routes of administration is that, in most cases, these treatments require long periods of therapy such as, for example, in some types of diabetes, for which treatment is needed for the entire life, the frequency of administration being daily. Non-oral administration is a great disadvantage mainly for the patient, and for this reason, it is important to look for alternative routes of administration.
Fundamentally, the oral route, which is the most convenient for the patient and the most economical, is preferred; however, for these types of molecules (mainly for oligosaccharides and proteins), designing formulations prepared to be administered by oral route entails a problem and involves many complications, since the gastrointestinal tract degrades these active compounds. This means that they should be formulated to enable, first, the pharmaceutical form to pass through the stomach without degrading the active compound, and once it reaches the optimum absorption mucosa, release a large quantity of this active compound selectively on the mucosa wall in a relatively short time interval. By doing so, the desired therapeutic or preventive activity is obtained.
In recent decades, numerous vehicles have been developed or designed to increase the systemic bioavailability after mucosal administration of numerous traditionally poorly absorbable active compounds, among which we highlight protein compounds, such as insulin (Norovirus capsid protein expressed in yeast forms virus-like particles and stimulates systemic and mucosal immunity in mice following an oral administration of raw yeast extracts. Xia et al. Journal of Medical Virology (2006), Volume Date 2007, 79(1), 74-83; Delivery systems and adjuvants for oral vaccines. Opinion on Drug Delivery (2006), 3(6), 747-762; Gastrointestinal absorption of heparin by lipidization or coadministration with penetration enhancers. Ross et al. Current Drug Delivery (2005), 2(3), 277-287); antigens (Gastrointestinal absorption of heparin by lipidization or coadministration with penetration enhancers. Ross, Benjamin et al. Current Drug Delivery (2005), 2(3), 277-28; Oral heparin: status review. Arbi et al. Thrombosis Journal (2006)) and antibodies, as well as polysaccharides such as unfractionated heparins and low molecular weight heparins (Ximelagatran. Choudhury et al. Drugs of Today (2006), 42(1), 3-19).
The following are examples of technologies developed to provide vehicles designed to increase systemic bioavailability after the mucosal administration of numerous active compounds which are traditionally poorly absorbable:                Design of prodrugs (Prodrug strategies to enhance the intestinal absorption of peptides. Gangwar et al. Drug Discovery Today (1997), 2(4), 148-155.)        Use of enzyme metabolism inhibitors (Pharmacokinetic enhancement of protease inhibitor therapy. King et al. Clinical Pharmacokinetics (2004), 43(5), 291-310).        Development of absorption promoters (Patent EP1652836; patent IS 200602146).        Development of mucoadhesive devices such as bioadhesive systems or intestinal patches (Oral delivery of macromolecules using intestinal patches: applications for insulin delivery. Journal of Controlled Release (2004), 98(1), 37-45).        Development of particulate systems        
Bioadhesive systems are structures of relatively large size which adhere to the intestinal mucosa after oral administration, thereby significantly increasing the time of intestinal transit of the formulation. Likewise, these devices avoid, to a large extent, the need for the active compound to diffuse through the luminal environment or even through the mucosa coating the absorption epithelium. An example of these systems is the development of bioadhesive patches, developed for the first time for the systemic absorption of active compounds in the intestine by Eaimtrakarn et al. (Retention and transit of intestinal mucoadhesive films in the rat small intestine. Eaimtrakarn et al. International Journal of Pharmaceutics (2001), 224, 61-67) which consists of a four-layered device: (I) a film of coating formed by a water-insoluble polymer which protects the protein active principles from luminal degradation, (II) a surface constituted by a polymer sensitive to the intestinal pH, (III) an intermediate film carrying the active compound and (IV) a bioadhesive film positioned between the intermediate film and the surface coatings designed to generate a high concentration gradient between the patch and the intestine enterocytes. However, these devices are affected by physiological processes of cell and mucosal turnover in the absorption epithelium. It is for this reason that the use of these devices has not yet managed to avoid the serious problem of variability between administrations, both in relation to the place of adhesion and the contact time of the formulation with the absorption membrane.
To summarize the above, current research in pharmacology (based on particulate systems) is focused on two different but complementary areas: targeting and controlled release systems.
The release profile of the active compound depends on numerous parameters: size, distribution, porosity, degradation, permeability of the polymer, etc.
The administration of a free drug by oral, intravenous route, etc., normally gives rise to a systemic distribution of the active compound, when what is affected is only a tissue, a local area or a type of cell. From this perspective, it would make much more sense to achieve a targeted action of the drug, especially for those compounds with high toxicity (such as anti-carcinogenic) or for those with a low therapeutic index. For example, administration through these particulate release systems involves an improvement in the administration of the anesthetic agents, reducing the necessary number of doses, avoiding systemic toxic effects and increasing its concentration in the desired site (Le Cone, P., Rytting, J. H., Gajan, V., Chevanne, F., Le Verge, R., J. Microencapsulation, 14 (1997) 243 Blanco, M. D., Bernardo, M. V., Gomez, C., Muñiz, E., Teijón, J. M., Biomaterials, 20 (1999) 1919.; Estebe, J. P., Le Corre, P, Chevanne, F., Malljdant, Y., Le Verge, R., Anesth. Analg. 81 (1995) 99).
As to controlled release systems, particulate vectors are formed by polymeric elements which control the release and/or absorption of the active compound through different mechanisms, within which the most typical are the diffusion of the active compound through the pores or channels formed in the polymeric matrix and the degradation/erosion of the polymeric material.
U.S. Pat. No. 6,475,493 discloses formulations that provide a controlled release in acidic media and quick/rapid release in basic media. The formulations employ cores with aqueous coatings which comprise, in heterogeneous mixture: a) at least one water insoluble polymer in a proportion of 75% by weight of the coating; b) an enteric water soluble polymer at pH higher than 6.0 in a proportion of 1-25% by weight of the coating; and c) a water-soluble polymer.
The heterogeneous degradation of the polymeric material occurs on the surface of the material which is in contact with the physiological medium. In this case, the rate of degradation is constant and the undegraded material maintains its chemical integrity during the process. Logically, those materials with high surface/volume ratio will degrade faster than the equivalents with a smaller ratio.
Homogeneous degradation involves a random deterioration throughout a polymeric mass. Whilst the molecular weight of the polymer continually decreases, the material can maintain its original shape and retain mass until the polymer has undergone a considerable degradation (even more than 90%), and reaches a critical molecular weight; at that time the solubilization and loss of mass starts (Sáez et al. Liberación Controlada de Fármacos. Revista Iberoamericana de Polímeros. Vol 5(1). 2004).
U.S. Publication 2005/0020539 A1 discloses pharmaceutical compositions, and methods of preparation thereof, for the oral administration of heparin for its selective release in the intestine. The compositions comprises a structure of multiple matrices which comprises: a) an internal matrix of amphiphilic compounds and lipophilic compounds wherein the active compound is at least partially embedded; and b) an outer hydrophilic matrix within which the internal matrix is dispersed.
For drug-containing particles to have the desired activity, homogenous degradation throughout the polymeric mass is preferred in order to achieve a suitable release. Also, a suitable surface potential should be favored so that the particles approximate the absorption mucosa. Currently the effort of large multinational companies in the pharmaceutical sector is focused on the development of colloidal systems with reduced particle size, as a strategy to increase the systemic bioavailability of active compounds.
It is very well known in scientific literature and in the patent state of the art, how reduced particle size significantly increases the dispersion of the active compound on a large luminal surface, favoring a controlled release of the drug (Potential of poliester microparticles for the sustained release of oral vaccine. Benoit, M. et al. Biopharmaceutics and Pharmaceutical Technology, 1st, Budapest, May 9-11, 1995 (1995), 431-2), decreasing the local concentrations of active compound and enabling high mucoadhesion (Preparation of thiomer microparticles and in vitro evaluation of parameters influencing their mucoadhesive properties. Albrecht, K.; et al. Drug Development and Industrial Pharmacy (2006), 32(10), 1149-1157), as well as the systemic passage of whole particles (Intestinal absorption of PLGA microspheres in the rat. Damge, C. et al. Journal of Anatomy (1996), 189(3), 491-501) which release the active compound in a controlled manner. Studies carried out by numerous authors reveal the potential shown by these devices for improving intestinal absorption of poorly absorbable molecules, as well as showing the importance of small particle size in intestinal absorption (Transmucosal macromolecular drug delivery. Prego, C. et al. Department Journal of Controlled Release (2005), 101(1-3), 151-162; Gastrointestinal uptake of biodegradable microparticles: effect of particle size. Desai et al. Pharmaceutical Research (1996), 13(12), 1838-1845).
These colloidal systems include microparticles (Polymeric nano- and microparticle technologies for oral gene delivery, Bhavsar et al. Expert Opinion on Drug Delivery (2007), 4(3), 197-213); nanoparticles (Lectin-modified solid lipid nanoparticles as carriers for oral administration of insulin, Hang et al. International Journal of Pharmaceutics (2006), 327(1-2), 153-159); formation of complexes (Stable pharmaceutical formulations comprising macromolecular carriers and methods of use thereof, Tan et al. WO2007021970) and liposomes (Investigation of lectin-modified insulin liposomes as carriers for oral administration, Zhang et al. International Journal of Pharmaceutics (2005), 294(1-2), 247-259) among others.
Microparticles are spherical or non-spherical particles, preferred having a diameter below 125 μm. This group includes microcapsules, which are defined as vesicular systems wherein the drug is confined to a cavity surrounded by a single membrane (typically polymeric); and microspheres, which are matrix-based systems in the form of spherical particles with a size between one and several dozens of microns, without distinction between coating and core, wherein the drug is dissolved or dispersed within the matrix formed by support materials, generally biocompatible polymers and with a large spectrum of release rates and degradative properties (Torrado, J. J., Cadórniga, R., Vectorización, CIF, 8 (1989a) 242). The drug is released through various mechanisms, such as surface erosion, the degradation/dissolution of the matrix materials, diffusion, and a combination of diffusion and erosion or erosion and degradation (Torrado, J. J., Cadórniga, R., Farm. Clin., 6 (1989b) 724).
Nanoparticles are submicronic particulate systems (<1 μm). Depending on the process used to prepare nanoparticles, nanocapsules or nanospheres can be obtained, these being the morphological equivalents of microcapsules and microspheres, respectively (Rollot, J. M., Couvreur, P., Roblot-Treupel, L., Puisieux, F., J. Pharm. Sci, 75 (1986). 361-364).
An article (Oral bioavailability of a low molecular weight heparin using a polymeric delivery system, Journal of Controlled Release 2006, 113, 38) describes nanoparticles formed by a technique of multiple emulsion and evaporation of solvent, which nanoparticles contain a dispersion of tinzaparin in a polymeric matrix of poly (c-caprolactone) and Eudragit® RS and contains polyvinyl alcohol as surfactant.
Another article (Microencapsulation of Low Molecular Weight heparin into Polymeric Particles Designed with Biodegradable and Nonbiodegradable Polycationic Polymers, Drug Delivery 2003, 10, 1) describes microparticles formed by the method of water/oil/water emulsion and evaporation of solvent, which contain low molecular weight heparin, biodegradable polymers such as poly(c-caprolactone) or poly(D,L-lactic acid-co-glycolic acid) and nonbiodegradable polycationic polymers such as Eudragit® RS or Eudragit® RL) or Eudragit® RS: poly(c-caprolactone) combinations; Eudragit® RS: poly(D,L-lactic acid-co-glycolic acid); Eudragit® RS: Eudragit® RL: poly(D,L-lactic acid-co-glycolic acid) (PLGA) wherein the polymers are present in equal proportion. Due to the hydrophilic nature of the active substance (low molecular weight heparin (LMWH)) an important diffusion of the active substance is induced through the continuous aqueous phase during the emulsification and solidification procedure. For this reason, the resulting particles have a variable distribution of the active substance through the particle, always having, in a greater or lesser proportion, active substance on the surface. Taking into consideration that they are small-sized particles which have a high specific contact surface with the gastric acids and enzymes, this aspect means that part of the active compound is lost in its passage through the stomach. Furthermore, microparticulate systems, which intrinsically bear a low content of active substance, have a lower encapsulation yield than particles of larger size. Therefore, the amount of active substance they can incorporate is small.
U.S. Publication 2005/0013866 A1 (whose inventors are co-authors of the article mentioned in the previous paragraph) discloses nanoparticles and microparticles for the oral administration of heparins, peptides and proteins, nucleic acids and growth hormone, formed from a polymeric matrix which comprises at least one biodegradable polymer with at least one polycationic polymer. The biodegradable polymer may be selected from polyesters, poly-ε-caprolactone, polyanhydrides, polyamides, polyurethanes, polyacetals, polyorthoesters and natural polymers and the polycationic polymer may be selected from cellulose derivatives, copolymers of acrylic and methacrylic acid esters such as trimethylammonioethyl methacrylate chloride, chitosan and derivatives and polylysine. The particles are obtained by formation of a water/oil/water emulsion.
The great advantage of these micro- and nanoparticulate systems compared with alternative solutions such as implants is that, due to their small size, they can be injected with a conventional syringe, not requiring surgical intervention. On the other hand, and although it seems paradoxical, it may be easier for a microsphere to be introduced in a cell than for the free drug, since a nanoparticle or microparticle of suitable size is easily incorporated as a vacuole through phagocytosis.
These systems are very interesting as drug carriers which cannot be reproducibly or reliable administered orally, for drugs such as protein, peptide, hormone or enzyme drugs which are the product of the biotechnological revolution, and are easily degraded by the gastrointestinal tract enzymes. Furthermore, polymeric microparticulate systems incorporating anti-carcinogens have been described and clinically tested (Wood, R. W., Li, V. H. K., Kreuter, J., Robinson, J. R., Int. J. Pharm., 23 (1985) 175); immunosuppressants (Yoshikawa, H., Nakao, Y., Takada, K., Muranishi, S., Wada, R. T., Tabata, Y., Hyon, S. H., Ikada, Y., Chem. Pharm. Bull., 37 (1989) 802.); vitamins (Sánchez, A., Vila-Jato, J. L., Alonso, M. J., Int. J. Pharm., 99 (1993) 263); antibiotics, antibacterial agents (Sánchez, A., Vila-Jato, J. L., Alonso, M. J., Int. J. Pharm., 99 (1993) 263); anti-inflammatory agents (Dubemet, C., Benoit, J. P., Couarraze, G., Duchène, D., Int. J. Pharm., 35 (1987) 145.) and vaccines (Eldrige, J. H., Staas, J. K., Meulbrock, J. A., McGhee, J. R., Tice, T. R., Gilley, R. M., Mol. Immunol., 28 (1991) 287) with very good results.
Among all of them, nanoparticles (particulate vectors with a diameter below 1 μm) have shown the greatest potential mainly due to the advantages conferred by their reduced size (Nanoencapsulation. II. Biomedical applications and current status of peptide and protein nanoparticulate delivery systems. Reis et al. Nanomedicine (2006), 2(2), 53-65). These devices may be prepared using polymers such as albumin, ethyl cellulose, gelatin, casein, polyesters, polyanhydrides, polyalkylcyanoacrylates and natural polymers among others (Polymeric nano- and microparticle technologies for oral gene delivery. Bhavsar et al, Expert Opinion on Drug Delivery (2007), 4(3), 197-213; Starch microparticles as vaccine adjuvant. Rydell et al. Expert Opinion on Drug Delivery (2005), 2(5), 807-828) through procedures such as solvent evaporation/extraction (Polymeric nano- and microparticle technologies for oral gene delivery. Bhavsar et al. Expert Opinion on Drug Delivery (2007), 4(3), 197-213); interfacial polymerization; simple coacervation (Polymeric coacervate microparticles useful for the sustained release administration of therapeutic agents. Heller, Phillip F. WO2006023207; Encapsulation of adenoviral vectors into chitosan-bile salt microparticles for mucosal vaccination. Lameiro et al. Journal of Biotechnology (2006), 126(2), 152-162), complex coacervation (Chitosan: An Atractive biocompatible polymer for macroencasulation. C. Peniche et al. Macromolecules Bioscience, (2003) 3, 511-520; Tramadol release from delivery system based on alginate-chitosan microcapsules. Acosta et al. Macromolecules Bioscience, (2003) 3, 546-551) and precipitation of supercritical fluids (Drug delivery applications of supercritical fluid technology. Sunkara et al. Drug Delivery Technology (2002), 2(1), 44, 46-50), among others.
The advantages conferred by the reduced particle size in the increase of absorption of poorly permeable molecules through the mucosal barrier can be found in numerous publications in the scientific literature (Mucoadhesive nanoparticulate systems for peptide drug delivery. Takeuchi et al. Advanced Drug Delivery Reviews (2001), 47, 39-54; Enteral absorption of insulin in rats from mucoadhesive chitosan-coated liposomes. Takeuchi et al. Pharmaceutical Research (1996), 13, 896-901).
The research carried out by Morishita et al. (Mucosal insulin delivery systems based on complexation polymer hydrogels: effect of particle size on insulin enteral absorption. Morishita et al. Journal of Controlled Release (2004), 97, 115-124) clearly shows the degree in which the reduction in particle size increases systemic bioavailability of insulin when the formulations are administered intestinally. According to published observations by these authors, a reduction in particle size from 180-230 μm to <43 μm produces a 18 fold increase in the bioavailability not the insulin administered, going from a systemic bioavailability (relative to the subcutaneous route) of 0.7% to 12.8%.
However, these smaller size particulate systems have a series of drawbacks. For microspheres, the main obstacle to achieving effective parenteral systems is the degradation and subsequent non-specific elimination by the reticuloendothelial systems, despite the fact that attempts have been made to modify these systems appropriately (Davis, S. S., Ilium, L., Colloidal delivery systems-Opportunities and challenges. Site-Specific Drug Delivery, E. Tomlinson, (S. S. Davis (Eds), pp. 93-110 (1986), John Wiley & Sons Ltd.; UK). This aspect worsens in the case of oral route administration, since in this case it has been verified how degradation at stomach acid pH makes the active compound reach the site at which it should be absorbed in very small quantities, causing up to 90% losses in in vitro activity.
For polymeric conjugate transport systems, their low solubility usually causes problems in their preparation (Duncan, R., Kopekova-Rejmanova, P., Strohalm, J., Hume, I., Cable, H. C., Pohl, J., Lloyd, B., Kopecek, J., Br. J. Cancer, 55 (1987) 165-174.; Endo, N., Umemoto, N., Kato, Y., Takeda, Y., Hara, T., J. Immunol. Methods, 104 (1987) 253-258) and in their injection into the blood stream (Zunino, F., Pratesi, G., Micheloni, A., J. Control. Rel., 10 (1989) 65-73).
Other forms of release of active compounds are micelles which, although they are one of the least studied systems, they base their activity on physicochemical characteristics, especially in organic solvents (Chu, B., Langmuir, 11 (1995) 414-421). Currently, there are water-soluble micelles related to the chemistry of amphiphilic polymers, which are biocompatible and biodegradable. However, these formulations have limitations with regards to the stability of the active compound to be released.
Homar et al (J Microencap 2007, 24:7, 621-633) have studied the influence of polymers on the bioavailability of microencapsulated celecoxib. Microparticles with a size range of 11-34 micrometers were prepared using an emulsion method followed by solvent evaporation. Relative bioavailability of celecoxib was below 20% in all cases.
On the other hand, the use of technologies linked to the production of nanoparticles and microparticles is currently limited by a considerable number of factors which limit the subsequent clinical and industrial development thereof. Among the factors which limit the use of these technologies are: a) complex preparation processes; b) problematic scale-up (Microspheres for controlled release drug delivery. Varde, et al. Expert Opinion on Biological Therapy (2004), 4(1), 35-51); c) limitations in medium and long-term stability (Strategic approaches for overcoming peptide and protein instability within biodegradable nano- and microparticles. Bilati et al. European Journal of Pharmaceutics and Biopharmaceutics (2005), 59(3), 375-388); d) high development and production costs; e) low bioavailability of the pharmaceutical active with these types of systems (particle size lower than 100 μm; see Issues in oral nanoparticle drug carrier uptake and targeting. Florence, Alexander T. Journal of Drug Targeting (2004), 12(2), 65-70); the best results being obtained in the administration of molecules with immunological properties wherein the nanoparticles and the microparticles of smaller size have intrinsic activity as antigenic adjuvants; see Potential of polymer microencapsulation technology for vaccine innovation. Morris et al. Vaccine (1994), 12(1), 5-11; Particulate systems as adjuvants and carriers for peptide and protein antigens. Liang et al Current Drug Delivery (2006), 3(4), 379-388)).
Nanoparticle systems also have problems with low product yield and low encapsulation efficiency. The use of emulsions and/or interfaces in many of the devices based on microparticles and nanoparticles enables the release/migration of the drug substances to into the process liquids or media which will later be eliminated as part of the preparation process, thereby causing a very high loss of active compound. In the same way, the preparation processes can generate numerous losses of the matrix-forming material, of the matrix or of the particle coating. The loss of polymeric material in the filters used in the preparation of microparticles by evaporation/solvent extraction and losses by adhesion of matrix-forming material in the preparation of microparticles, for example as can occur with spray drying.
Nanoparticle systems also suffer from poor batch-to-batch reproducibility. The special sensitivity of colloidal systems to small variations in the particulate vector preparation conditions requires a strict control of all manufacturing variables, paying special attention to environmental factors (temperature, humidity, atmospheric pressure), variations in the excipients or starting materials as well as in the instruments used in their preparation. By way of example, a small increase in the preparation temperature favors the diffusion of the active compound incorporated in the internal phase of a w/o/w (water/oil/water) emulsion towards the external aqueous phase, thereby causing a great loss in active compound content. All these conditioning factors usually cause great batch-to-batch variations in particular in: a) the release profile of active compound from the nanoparticles; b) requirement of excessively broad product specifications; and c) residual solvent content.
Small variations in the preparation conditions or the starting materials may cause large variations in the active compound content of these formulations, thereby severely hindering the standardization of the process within acceptable limits Likewise, variations in the active compound content as well as in the particle size of these formulations (fundamentally due to small variations in the stirring conditions and to environmental variations) cause changes in the release of the active compound from these vectors. Thus, an increase in particle size will delay the release of the active compound, modifying its pharmacokinetic profile after its administration and, therefore, its systemic bioavailability.
The batch-to-batch variability, due to the sensitivity of these systems to variations in the preparation conditions, forces establishment of very broad end product specifications in order to validate the production of a batch by a previously standardized industrial procedure. It may serve, for example, to establish specifications for parameters such as active compound content or the release of active compound in a determined time which, as previously indicated, have a large batch to batch variability.
The preparation of particulate systems by procedures such as interfacial polymerization and emulsification, with subsequent evaporation/solvent extraction, often requires the use of very high quantities of organic solvents, for which daily administration is limited based on the majority of the Pharmacopoeias existing at present. Despite the fact that the elimination of these solvents forms part of the preparation procedure of these vectors, the solvent avidity of some polymers typically used, the sensitivity of the particulate vectors to more efficient solvent elimination methods (such as, for example, lyophilization) and the reduced limits for the presence of some of the most commonly used solvents for the preparation of microparticles and nanoparticles (such as, for example, Dichloromethane, classified in the European and United States Pharmacopoeias as Class 2 solvent), may limit the clinical use of microparticles and nanoparticles.
Size-related toxicity of nanoparticles is also an issue. When particulate vectors are administered by mucosal routes, the active compound content therein may be released to the luminal environment by mechanisms already described herein, or the particulate vectors may fully cross the absorption membrane and subsequently release the active compound. In this regard, the particle size constitutes the most important parameter, since a reduction in particle size causes an exponential increase of the material in the form of particles which fully cross the mucosal barrier. In other words, the smaller the particle, the larger the relative proportion of mass of powder or colloid that is attributable to the excipients rather than the active (Gastrointestinal uptake of biodegradable microparticles: effect of particle size. Desai et al. Pharmaceutical Research (1996), 13(12), 1838-1845)). Unlike larger sized particulate vectors, as may be the case of granules and pellets prepared with polymers, the absorption of the microparticle-forming material and, especially of nanoparticles, requires consideration of the toxicological aspects related to the delivery of these materials to systemic circulation. Likewise, the consequences of the exposure of potentially antigenic materials on the immune response (such as, for example, proteins) in the form of microparticles and nanoparticles on organs, tissues or bodily compartments to which immunocompetent cells may access are known, it being possible to generate a wide range of immune responses ranging from the suppression of lymphocyte proliferation to the appearance of hypersensitivity reactions.
There are a high number of procedures for the preparation of systems in the form of microparticles and nanoparticles which are currently protected by patents. Likewise, the need to use high solvent quantities, high gas pressures, the establishment of sophisticated control methods of the manufacturing conditions, the high cost of the machinery used and the little presence of these formulations in the market are conditioning factors, known by a person skilled in the art, which raise production costs and condition the existence of facilities which have sufficient manufacturing flexibility to manufacture by contract formulations of this type, also worsened by the complexity in the scaling of the formulations of microparticles and nanoparticles developed in the laboratory.
All these factors have limited commercialization of nanoparticle-based products and highlight the need to develop vehicles which involve less aggressive manufacturing methods, which have improved stability properties and whose industrial scaling is possible or executable by procedures more commonly used in the pharmaceutical industry.
Despite the fact that the use of granules and pellets has been primarily for the oral administration of active compounds, the current state of the art demonstrates that no formulation constituted by them, nor any other derivative thereof such as capsules or tablets, has managed to give rise to significant absorptions of macromolecules whose systemic bioavailability after their non-parenteral administration is more limited by the reduced permeability in the absorption barrier of the molecule than due to the reduced solubility thereof in the luminal fluids.
U.S. Publication 2005/0281871 A1 discloses a spray coating method for coating granules or pellets wherein the mixture of coating components is performed during the spray process, by simultaneous spray of two aqueous dispersions containing the film forming agents separately, said agents being selected from: a) a (meth)acrylate C1-C4 alkyl ester or methacrylic acid in a 30-80% by weight and (meth)acrylate monomers bearing a tertiary amino group in the alkyl radical in 70-20% by weight; and b) a polymer bearing anionic groups selected from cellulose derivatives or (meth)acrylate copolymer. This overcomes problems related to the formation of dispersed mixtures by spray coating, such as aggregation or coagulation of components and the use of non ionic emulsifiers in 10% by weight and higher, which homogenize the dispersions but presents as a drawback an increase in active compound instability.
Therefore, it can be concluded that the latest advances in pharmaceutical technology of oral formulations containing active compounds of the types previously described herein, irrespective of the problems which may be associated to the industrial preparation process, are aimed at increasing the contact surface by adhesives or reducing particle size. These favor contact by increasing their specific surface to achieve significant absorptions of active compounds through the mucosal routes. Particulate systems of greater size are left to one side because the surface potential thereof cannot be calculated (which entails a problem since the surface charge of the particles cannot be calculated to be able to predict the approximation and non-repulsion thereof with the mucosal surface) nor can they be phagocyted (phagocytosis by cells) due to their greater size and to the difficulty of those particles with greater specific surface area to adhere to the mucosa while avoiding repulsion from the very same mucosa. The inventors have previously observed that when the pharmaceutical dosage forms of the prior art were used in greater size, the absorption decreased.
Considering the existent prior art discussed herein, it would not be expected that a person skilled in the art, would be inclined to develop systems of large particle size made through common and easily standardizable processes and to achieve significantly high systemic bioavailability of drugs for which the mucosa route has been traditionally inaccessible, by improving the release as well as the absorption of said drug(s). There remains, therefore, the need to provide new particulate systems for the administration of active compounds via mucosal route.